Superheater



Jan. 29, 1929.

A. D. PRATT SUPERHEATER Filed oct. 15, 1921 NVENTR. 9- Kaz* bu Gua A TTORNEYS.

Patented Jan. 29, 1929.`

UNITI-1D STATES 1,700,237 PATENT OFFICE.

ARTHUR D. PRATT, OF SHORT HILLS, NEW JERSEY, ASSIGNOR TO THE IBABCOCK & WILCOX COMPANY, F BAYONNE, NEW JERSEY, A CORPORATION OF NEW JERSEY.

SUPERHEATER.

Application filed. October 15, 19,21. Serial No. 507,946.

My present invention relates to superheaters, particularly superheaters applied to boilers of the well-known Babcock & Wilcox type having headers connected by horizontally inclined tubes.

My invention will best be understood from the following description and the drawing which shows a vertical section of a horizontal tube type boiler having one 'form of my invent'ion applied thereto, only the upper portion of the boiler being shown.

In the drawing, 10 are the horizontally inclined boiler tubes connected to uptake headers 11 and downtake headers 12. The headers 12 and11 are connected by nipples 13 and tubes 14,\respectively,vto a steam and water drum 15. Cross baiies 16 and y17 are arranged, as usual, to provide the boiler with three cross passes, the first upward pass being between the headers 11 and the baiie 16, the second or downward pass being between the baffles 16 and 17, and the last upward pass between the baiiie 17 and the headers 12. The gases pass out of the gas outlet 18. The batiie 17 is continued upward above the tubes 10 to form part of the gas outlet. y.

The superheater, which I have illustrated, is provided with a pair of horizontally disposed, parallel headers extending crosswise.

of the tubes 10. The inlet header 19 is located'adj acent the boiler headers 12, and the outlet header 20 is located outside of the last passof the boiler, and preferably adjacent the tubes 14. The connection to theinlet header is indicated at 191 and the outlet connection from the header 20 is indicated at 201. p

Connecting the headers 19 and 20 are the superheater tubes, which, in the form illustrated, are arranged in pairs. These tubes have ageneral U'shape and extend to a point adjacent the uptake headers 11.

As will be seen from the drawing, the superheater tubes extend substantially'the full length of the water tubes 10, or, /in other words, extend substantially Yfrom the boiler headers 12 to the boiler headers 11. The hot gases passing through the first pass of the boiler pass around the upper end of the bathe 16, so that the entire length of the superheater tubes between the baiiie 17 and the headers 11 are contacted thereby. The gases passing to the outlet 18 also Contact with the portion of the tubes between the baiiie 17 and the headers 12.

` Heretofore in superheaters, it has been desirable to make the legs of the U-shaped superheater tubes of substantiall the same length to prevent undue distortion and unequal strains on the two headers which might be caused by the unequal heating of the two legs of the tubes. T his has restricted the possible length ofthe superheater tubes, and therefore the amount ot' superheat which might be obtained when the superheater is located above the boiler tubes.

By my arrangement, I am enabled to make the superheater tubes as long as desirable in order to obtain the desired amount of superheat, and at the same time, to avoid difficulties which would ordinarily arise by reason of the unequal length or the unequal heating of the legs of the superheater.

In the form illustrated, the lower and longer leg of the U tubes is provided with a number of substantially parallel straight portions preferably connected by at least two reverse bends. The upper leg 21 is substantially straight and is connected by a bend 25 with a straight portion 22 otl the lower leg, which, in turn, iseonnected .by a bend 26 with a substantially parallel portion 23. 'The portion 23 is, in turn, connected by a bend 27 with another substantially parallel portion 24. Allv of the straight portions have a slightly downward slope, so that any water which may enter the superheater will drain downward toward the inlet header 19.

Preferably, I proportion the two legs of the superheater so that when such legs are affected by the heat from the steam passing through them, and also by the hot gases contaoting with the exterior thereof, the eXpansion of the two legs will be substantially uniform. By placing the inlet header at the lower point, it will be obvious that the steam passing through the lower leg of the superheater tubes will be cooler relatively than the steam passing through the upper leg. Similarly, by locating the superheater in the manner shown, the longer lower leg will be contacted for a portion of its length by gases which are cooler than the gases which contact with the upper leg of the U. By proportioning the several sections of the legs of the U and loca-ting them in defined relation to the hot gases, I provide a superheater in which each leg will have substantially the same amount of longitudinal extension for a given set of conditions. By providing the return portion 23 substantially parallel to the `the tube above 100 temperature would be about -flg of an inch.

straight portions 22 and 24, it will be seen that the total extension of the lower leg will be, in substance, the algebraic sum of the extensions of the several parts. Moreover, by reason ofthe plurality of bends which I have provided, any difference in the amount of extension of the two legs will be taken up in these bends without subjecting the headers to non-uniform strains.

The following is given as an example of the manner in which the several parts of my superheater tubes may be proportioned: The straight portion 21 may be101/2 feet long; the straight portion 22 may be 12 feet long; the straight portion 23 may be 3 feet long; the straight portion 24 may be 7 feet long. Now, with such a superheater, if saturated steam at 200 pounds pressure enters the inlet box, and steam at 200o superheat leaves the outlet box, the average temperature for the straight portion 24 ofthe superheater would be approximately 406, and an expansion of due to this increase in The straight portion 23 would average approximately 437, with an expansion of about g3g of an inch. The straight portion 22 would average approximately 485, with a resulting expansion of about of an inch. The algebraic sum of these expansions of the parts forming the lower leg would, therefore, be approximatelyof an inch.

The straight portion 21 would have an average temperature of approximately. 551,

with a resulting expansion of about of an inch. Therefore, under the conditions stated,

the difference inexpansion of the two legs of the tube would be only e of an inch, and it is obvious that this difference would be readily absorbed by the plurality of bends which I have rovided.

Whlle, preferably, I provide the longer leg of the U tube with the return bend illustrated,

it will be obvious that my superheater may be arranged without this return bend, if the conditions under which the steam enters and leaves the superheater tubes, and the condi- -tions under which the hot gases Contact with the respective legs of the tubes are such as to equalize the expansion of the two legs, even if one be longer than the other.

It will also be obvious that, if desired, a larger number of approximately straight portions connected by bends may be provided and that, if desired, a return bend may be' inserted in the upper leg of the U tube as well as in the lower leg.

It will also be understood that, while I have illustrated my invention in4 connection with a boiler of a certain type, I do not intend to be limited to that, since my invention can be applied to many dierent types of boilers.

1. In combination, a. steam boiler and a4 superheater having parallel inlet and outlet headers and tubes of a general U necting the headers and contacted by the hot gases of the boiler, the legs of the U being of substantially unequal length with the longer leg connected to the inlet header andthe shorter leg connectedto the outlet header, the relative lengths of the legs beingsuch that the longitudinal extension due to the heat of the steam in each leg and of the gases in contact therewith is substantially the same in each leg.

2. In combination, a steam boiler and a superheater having parallel inlet and outlet headers and tubes of a general U shape connectinfr the headers and arranged in relation to therboiler so that the hot gases iow generally from the bend of the U toward the headers, the legs of the U being of Substantially unequal length 'with the longer leg connected to the inlet header and the shorter leg connected to the outlet header, the relative lengths of the legs being such that the shape conlongitudinal extension due to the heat ofthe steam in each leo and of the gasesv in contact therewith is sdbstantially the same in each leg.

3. A superheater having parallel inlet and out-let headers connected by tubes extending from each header in the same general direction, the tubes having a plurality of bends connected by straight portions extending in the same general direction and the tubes being located in a ygas passage arranged to direct hot gases generally from the part of the tubes most remote from the headers toward the headers, the connections of the steam supply to the headers and the lengths and arrangement of the straight portions of the tubes being such that the algebraic sum of the longitudinal extensions of the straight portions due to heat from the steam therein and the gases contacting therewith vis substantially zero.

4. In combination, a steam boiler and a superheater having parallel inlet and outlet headers vconnected by tubes of a general U- sh: pe' and having a plurality of bends therein connected by straight portions, the gas passage of the boiler in which the tubes are located being arranged so that the hot gases flow from the part of the tubes most remote from the headers toward the headers, the connections of the steam supply to the superheater and the lengths and arrangement of the straight portions of the tubes being such that the total longitudinal extension from Athe heat of the steam therein and the gases llt leu

ing across the boiler tubes and superheater' tubes connecting the headers, the superheater tubes being of a general U shape and extending lengthwise of the boiler tubes and arranged to be contacted by the hot gases passing from the first to the second pass of the boiler, the headers of the superheater being connected to the steam supply t cause the tacting therewith.

6. In combination, a steam boiler having horizontally inclined water tubes and cross baffles. therefor to provide cross passes,'and

la superheater above the water tubes, said superheater having parallel headers extending across the boiler tubes and connected by superheater tubes of a general U shape torming two legs of unequal length, the longer leg having at least two reverse bends, the tubes extending lengthwise of the boiler -tubes and arranged to be contacted by the hot gases passing over the baffles between the boiler passes, at least one of the legs of the superheater tubes extending over and being contacted by the gases from all of the passes of the boiler, the longer leg beingl connected to the inlet header and having a 1portion contacted by gases ot lower temperature than those contacting any otherA portion of the superheater.

7. In combination, a steam boiler having horizontally inclinedy water tubes andvcross battles to provide cross passes for the hot gases across the tubes. and a U-tube superheater above the boiler tubes and having its tubes connected to inlet and outlet headers, said superheater tubes extending lengthwise ot' the boiler tubes and forming two legs of unequal length, the longer leg having portions lying in more passes than the 'shorter leg, said longer leg being connected to Said inlet header.

8. In combination,asteamboiler and asuperheater having parallel inlet and outlet headers and tubes of a general U shape connecting the headers and contacted by the hot gases of the boiler, the legs of the U being of substantially unequal length with the longer leg connected io the inlet header and the shorter leg connec ed to the outlet header, the relative lengtl s of the legs being such that the longitudinal extension due to theheat of the steam in eerh leg and of the gases in contact therewith is substantially the same ineach les, wardly whereby the tubes will drain down ward towards the inlet header.

' ARTHURD. PRATT.

and the legs of the U-tubes sloping down 

